The Big Rock plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
Mostly sunny
Mostly sunny; warmer
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Partly cloudy
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1° on Nov. 17, 1959, the coldest reading for this week of the year since 1887. Next is 3° in 1933.
Big Rock’s center stands about 710 ft above sea level. Within three miles the land runs from 670 ft to 770 ft, a difference of 100 ft: gently rolling country. The highest named summit within 15 miles is Johnsons Mound, about 900 ft, 9 miles northeast.
Under the town center the state geologic map shows Maquoketa Formation or Group (shale, limestone), from the Late Ordovician, 445 to 454 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 56×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale, limestone. Age: Late Ordovician, 445 to 454 million years old. About 14 mi of the line.
Dolostone, limestone. Age: Silurian, 422 to 445 million years old. About 5 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 447 to 459 million years old. About 4 mi of the line.
Dolostone. Age: Early Ordovician to Middle Ordovician, 459 to 487 million years old. About 1 mi of the line.
Sandstone, limestone, dolostone. Age: Middle Ordovician to Late Ordovician, 454 to 468 million years old. About 0.6 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
A raindrop that lands in Big Rock reaches the Gulf of America by way of Welch Creek, Big Rock Creek, the Fox River, the Illinois and the Mississippi: about 1,480 river miles.
Lake on the way: Peoria Lake.
1,190 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Big Rock; river miles along the main stem, rounded.
Big Rock has a hot-summer humid continental climate. Summer afternoons average 84° in July; winter nights fall to about 16° in January. A normal year brings about 28 inches of snow; with the rain, that comes to about 40 inches of water.
On November 14 Big Rock normally reaches 48° and falls to 32°. The record high is 74°, in 1971; the record low 9°, in 1916. The most rain on this date, 1.65 in, fell in 1926.
Normals 1991–2020 and records since 1887 at Aurora Water, 12 miles east. NOAA, through RCC-ACIS.
